The present invention relates to a dieselsoot filter with a catalytically active coating. The active substance of the coating is to be comprised of metal doped zeolite.
Exhaust fumes of Diesel engines usually contain contaminants. The emission of carbon monoxide and hydrocarbon is lower in Diesel engines owing to the excess of air, than the in case of an otto motor. On the other hand, the NOX discharge is in the range of admissable limits. A large problem relating to the ecology is the emission of soot particles by a diesel engine. Since diesel soot is actually a health hazard, owing to its content of higher molecular hydrocarbon or poly-condensed aromates, and since one can actually call those contaminates outright carcenogenic (content of 3.4 benzpyrene and nitroaromates) it is desirable to provide suitable technical steps for reducing the emission in the diesel exhaust fumes.
Prior experience has shown that engine engineering features by themselves are insufficient to obtain a significant reduction in soot emission. It has been tried, for example, to limit the soot emission through the installation of a filter into the exhaust channel, as shown, for example, in U.S. Pat. No. 4,329,162. By virtue of the soot collection process, the filter clogs with time, thus increasing the ram pressure in the exhaust system, thereby in turn reducing the engine power. It is, therefore, necessary, from time to time, to regenerate the filter by way of combustion of the soot. A thermal oxidation of the soot, however, occurs only at temperatures which are usually not obtained by diesel exhaust gases.
U.S. Pat. No. 4319869 describes supplemental heating of the filter as a possibility to support the ignition of the diesel soot on the filter. This, however, is an added complication of the system and leads ultimately to a higher energy consumption. The same is true for adding combustion aids into the combustion gas.
Using a catalyst is the most promising aspect for technical realization of reducing the ignition temperature of the soot on the filter. Catalysts of this kind are described for example in German printed patent applications 2,951,316 or 3,141,713 or European patent application 0,160,482. The use of a mixed oxide catalyst, indeed, decreases the ignition temperature of the soot, but a cleaning of the filter still will require temperatures which are simply unrealistic.